One example of a governor valve assembly according to the prior art regulates supply pressure in three stages in response to an increase in the rotational speed of an output shaft.
Reference will be had to FIGS. 1 through 4 to give a more detailed description of conventional governor valve assemblies to which the present invention appertains and of the shortcomings possessed by such governor valve assemblies.
A governor valve assembly of the type that regulates supply pressure in three stages with an increase in the rotational speed of an output shaft is disclosed in the specification of U.S. Pat. No. 3,943,956. The three-stage regulation of line pressure is performed by a single governor valve, as shown in FIG. 1. When the output shaft, shown at numeral 1, is rotating at low speed, a governor weight 2, secondary weight 3, shaft 4, valve 5, outer spring 6 and inner spring 7 move outward together with respect to the shaft 1. The resulting hydraulic pressure, which counterbalances the centrifugal force acting upon the governor weight 2, secondary weight 3 and valve 5 and an inwardly directed force acting upon the valve 5, constitutes governor pressure P.sub.G at the prevailing vehicle speed. This operation represents the first stage of pressure regulation.
When the rotational speed of the output shaft 1 rises and the shaft begins rotating in an intermediate speed region, the outward movement of the shaft 4 is checked by the governor body shown at numeral 8. Now the hydraulic pressure counterbalances the centrifugal force acting upon the secondary weight 3 and valve 5 and the forces applied by the outer spring 6 and inner spring 7. This hydraulic pressure is the governor pressure P.sub.G at the prevailing vehicle speed. This is the second stage pressure regulation.
At high speed rotation of the output shaft 1, the outward movement of the secondary weight 3 is checked by the governor weight 2, so that the hydraulic pressure prevailing from this point onward counterbalances the centrifugal force acting upon the valve 5 and the forces applied by the outer spring 6 and inner spring 7. The resulting hydraulic pressure is governor pressure P.sub.G. This represents the third stage of pressure regulation. The characteristic curve obtained by such three-stage pressure regulation effected by the governor valve assembly of FIG. 1 is illustrated in FIG. 2.
Another example of a prior-art governor valve assembly is as depicted in FIG. 3, in which two separate governor valves 10, 11 are arranged about the output shaft 1. In this arrangement, the governor valve 10 regulates pressure in response to an increase in the rotational speed of the output shaft 1, and the governor valve 11 is adapted to cut the governor pressure P.sub.G which prevails at low rotational speed. The resulting characteristic curve is as shown in FIG. 4.